Regulating power consumption of digital circuitry has become an important consideration in designing computing and consumer devices such as desktop and laptop computers, televisions, audio equipment, smartphones, cameras, etc. In portable devices, regulating power consumption helps increase the life of battery power, and in general, regulating power consumption helps reduce operating costs, particularly for large enterprise companies that may continuously operate hundreds or even thousands of computing and storage devices.
FIG. 1A illustrates a prior art gate speed regulator for regulating power consumption of digital circuitry including a critical path circuit 2. A propagation delay oscillator 4 generates a propagation delay frequency 6 representing a propagation delay of the critical path circuit 2. A frequency generator 8 generates a reference frequency 10 and a frequency comparator 12 generates a frequency error 14 representing a difference between the reference frequency 10 and the propagation delay frequency 6. An adjustable circuit 16, responsive to the frequency error 14, adjusts at least one of a supply voltage and a clocking frequency 18 applied to the critical path circuit 2 in order to maintain a target performance and/or a target power consumption.
For example, if the frequency error 14 indicates the propagation delay frequency 6 has fallen bellow a threshold, the adjustable circuit 16 may increase the supply voltage to the digital circuitry to maintain error free operation and performance by maintaining a target propagation delay. Alternatively, the adjustable circuit 16 may decrease the clocking frequency applied to the digital circuitry to maintain error free operation at a lower performance while decreasing the power consumption.
The propagation delay frequency 6 of FIG. 1A may be generated by a ring oscillator shown in FIG. 1B which comprises a plurality of inverters 200-20N connected in a ring configuration and an NAND gate 22 for enabling the ring oscillator in response to an enable signal 24. The output frequency of the ring oscillator depends on the number of inverters 200-20N, the amplitude of the supply voltage 18, and other factors, such as variations in fabrication process, ambient temperature, etc.